Hard metal (Co bonded WC), developed in the thirties, which had been successful until today in numerous variants due to its good wear resistance, has always been the trigger for experiments to ductilize also non-carbide ceramics with metallic phases. Especially in the sixties during which the term "Cermets" was coined (c.f. e.g. "Structure and Properties of Cermets") Z. Metallkde., 59 (1968) 170) numerous experiments concentrated on oxide ceramics of which a reduction in brittleness would have drastically improved the prospects for increased technical application. The desired advantageous combination of good ductility and fracture toughness of metals with the excellent high temperature properties, the wear resistance and the hardness of ceramics, however, was unsuccessful in most cases. On the contrary, cermets even combined the negative properties of both classes of materials. One cause lies in the typically very bad wetting of oxide ceramics by liquid metals which causes, during liquid phase sintering, the metal phase to sweat out of the body. In order to prevent this, such composite bodies must be hot pressed or hot forged as for instance carried out in the system Al.sub.2 O.sub.3 --Al (UK-Patent 2,070,068A; U.S. Pat. No. 5,077,246). Another cause for the bad mechanical behavior can be sought in the characteristic microstructure of cermets which typically results from a powder metallurgical mixture of the two phases. The ceramic component is mainly embedded in the metallic matrix which often amounts to less than 20 vol % (c.f. e.g. "Processing of Al.sub.2 O.sub.3 /Ni Composites", J. Eur. Ceram. Soc., 10 (1992) 95). In metal bonded carbides or boride cermets the ceramic phase can additionally form a skeleton, however, the metallic properties usually dominate in most cermets ("Cermets", Reinhold Publ. Co., New York, 1960). Today only carbide combinations, especially TiC-Ni, are designated as cermets.
New strengthening concepts for ceramic materials are based on the introduction of a second phase into the ceramic matrix such that the positive properties of the ceramic are essentially retained. Examples are transformation toughenable ZrO.sub.2 particles ("Strengthening Strategies for ZrO.sub.2 -toughened Ceramics at High Temperatures", J. Mat. Sci. Eng., 71 (1985) 23) or SiC whiskers ("TZP Reinforced with SiC Whiskers", J. AM. Ceram. Soc., 69 (1986) 288) in an Al.sub.2 O.sub.3 matrix. At first, the inclusion of metals was considered unreasonable because, according to conventional composite theories, metals with low yield stress and low modulus of elasticity could not improve brittle ceramics especially with respect to their strength. Admittedly, it has been shown recently that this is not always the case ("Effect of Microstructure on Thermal Shock Resistance of Metal-Reinforced Ceramics", J. Am. Ceram. Soc. 77 (1994) 701 and "Metalle verbessern mechanische Eigenschaften von Keramiken", Spektrum der Wissenschaft, Januar (1993) 107). However, the strengthening effect is only achieved if the microstructure of the classical cermets is reversed, i.e. the ceramic material forms a rigid matrix which is premeated by a monocrystalline metallic phase. The designation "metcers" would in this case constitute a conceptual characterization of the reversal in microstructural components. Quite apart from the modified microstructure of these composites, it is also the significantly smaller quantity of the metal phase which is responsible for the improvement compared to conventional cermets. The metal embedded in the ceramic matrix has considerably better mechanical properties than it does in the "free" state, a phenomenon which seems to apply even for otherwise brittle intermetallic phases ("Metcers--A Strong Variant of Cermets", Cfi/ber. DKG 71 (1994) 301).
So far, a number of different methods have been used to produce these novel metal-ceramic composites, for example the directed oxidation of molten metals (DMO), where an Al/Al.sub.2 O.sub.3 composite grows on molten aluminum by way of oxidation in air (see e.g. "Formation of Lanxide TM Ceramic Composite Materials", J. Mat. Res. 1 (1986) 81 and "Directed Oxidation of Molten Metals" in: Encyclopedia of Mat. end Eng. (Ed. R. W. Cahn), Supplementary Vol. 2, Peramon, Oxford (1990) 1111). Other practicable methods are pressure-die casting ("Application of the Infiltration Technique to the Manufacture of Cermets", Rep. Dt. Keram. Ges., 48 (1997) 262-8) and the infiltration of porous ceramic preforms with molten metal ("Method for Processing Metal-Reinforced Ceramic Composites", J. Am. Ceram. Soc., 73 [2] 388-393 (1990). Gas-pressure infiltration provides a means of infiltrating non-wetting metals into the ceramic preform (see e.g. "Microstructure and Properties of Metal infiltrated RBSN Composites", J. Eur. Ceram. Soc. 9 (1991) 61-65). The metal is first melted in a vacuum and then, once the infiltration temperature has been reached--usually 100 to 200.degree. C. above the melting point--the ceramic preform is dipped into the molten metal and a gas pressure built up. This technique is also suitable for metals with high melting points, which cannot be infiltrated into the ceramic preform using the conventional pressure-die casting method, but is time-consuming and very expensive.
Another method of producing an Al.sub.2 O.sub.3 part permeated Al is based on reactive metal infiltration of ceramic preforms containing SiO.sub.2 (see e.g. Al.sub.2 O.sub.3 /Al Co--Continuous Ceramic Composite (C.sup.4) Materials Produced by Solid/Liquid Displacement Reactions: Processing, Kinetics and Microstructures", Ceram. Eng. Sci. Proc. 15 (1994) 104).
Composite parts containing Al and Al.sub.2 O.sub.3 can also be produced by means of thermite-based reactions (SHS: Self-Propagating High-Temperature Synthesis). A large number of such reactions have been investigated so far, all of which proceed according to the scheme: EQU MO+Al.fwdarw.Al.sub.2 O.sub.3 +M,
where M is a metal and MO the corresponding oxide (see e.g. "Combustion Synthesis of Ceramic and Metal-Matrix Composites", J. Mat. Synth. Proc. 2 (1994) 71 and "Thermodynamic Analysis of Thermite-Based Reactions for Synthesis of Oxide-B.sub.4 C Composites", J. Mat. Synth. Proc., 2 (1994) 217 and 227). As a result of the uncontrollable generation of heat (the reaction is highly exothermic) all SHS composites are porous, in homogneous and of coarse microstructure. As a result their strength seldom exceeds 100 MPa, which means their use as structural parts is out of the question.
Research in the field of materials has for a long time pursued the goal of substituting intermetallic compounds for metals in may areas, also in metal-ceramic composites. The intermetallic compounds of Al (aluminides) are especially in demand here due to their low specific weight, good high-temperature stability and their resistance to oxidation (see e.g. "Intermetallic Compounds", Mat. Res. Soc. Proc. Vol. 288, 1993). However, the powder-metallurgical production of aluminides with ceramic phases has up till now been very costly, since, on the one hand, the production of the aluminide powder is very expensive because of the extremely inert conditions required and, on the other hand, the powder can only be fully compacted by means of hot pressing, hot forging, hot extrusion, hot isostatic pressing, or explosive forming (see e.g. "Powder Processing of Intermetallics and Intermetallic Matrix Composites (IMD)" p. 93-124 in Processing and Fabrication of Advanced Materials for High-Temperature Applications--II, ed. V. A. Ravi et al, The Min. Met. Mat. Soc., 1993). Moreover, in all cases the aluminide constitutes the matrix, while the Al.sub.2 O.sub.3 is dispersed as particulate phase and makes up less than 50% of the volume (see e.g. "A Review of Recent Developments in Fe.sub.3 Al--Based Alloys", J. Mat. Res. 6 (1991) 1779 and "Powder Processing of High-Temperature Aluminide-Matrix Composites", H-T Ordered Intermetallic Alloys III, 133 (1988) 403). For the production of such composites, use can be made of the reaction heat by having two or more metals react with each other to form the desired aluminide, but in all cases investigated so far this procedure results in coarse and inhomogeneous microstructures, which means that mechanical properties were either not measured at all ("Reactive Sintering Nickel-aluminide to Near Full Density", PMI 20 (1988) 25), or that, in a further step, the preformed part had to be subjected to hot post compaction ("SHS of TiAl--SiC and TiAl--Al.sub.2 O.sub.3 Intermetallic Composites", J. Mater. Sci. Let., 9 (1990) 432).
All hitherto know forms of composites and the methods of production thereof have characteristic disadvantages. The pressure-die casting technique, for example, is for technical reasons (no suitable pressure-vessel material available) only suitable for Al alloys, not, however, for high-melting-point aluminides. Similar limitations apply to gas-pressure infiltration, where aluminides can only be infiltrated at temperatures far in excess of 1400.degree. C. Moreover, in this case the infiltrated composite part would still have to be machined from the solidified aluminide melt, an extremely tedious procedure and only possible for parts with simple geometry. Reactive-type processes such as DMO and C.sup.4 can only be used for Al.sub.2 O.sub.3 parts with Al alloys containing Si or Mg, i.e. not for alloys containing aluminides. Besides, the reaction velocities are extremely low, averaging only 2 cm/day, which means that the procedure is extremely time-consuming. All powder-metallurgical processes used hitherto have resulted in the disadvantages typical of oxide-ceramic cermets, i.e. without subsequent hot compaction, the microstructure is porous, coarse (microstructural features usually being much larger than 10 .mu.m) and inhomogeneous, which results in inadequate strength as well as brittleness.